In recent years, there has been development of organic semiconducting (OSC) materials in order to produce more versatile, lower cost electronic devices. Such materials find application in a wide range of devices or apparatus, including organic field effect transistors (OFETs), organic light emitting diodes (OLEDs), organic photodetectors (OPDs), organic photovoltaic (OPV) cells, sensors, memory elements and logic circuits to name just a few. The organic semiconducting materials are typically present in the electronic device in the form of a thin layer, for example of between 50 and 300 nm thickness.
One particular area of importance is organic photovoltaics (OPV). Conjugated polymers have found use in OPVs as they allow devices to be manufactured by solution-processing techniques such as spin casting, dip coating or ink jet printing. Solution processing can be carried out cheaper and on a larger scale compared to the evaporative techniques used to make inorganic thin film devices. Currently, polymer based photovoltaic devices are achieving efficiencies above 8%.
However, the polymers for use in OPV or OPD devices that have been disclosed in prior art still leave room for further improvements, like a lower bandgap, better processability especially from solution, higher OPV cell efficiency, and higher stability.
Thus there is still a need for organic semiconducting (OSC) polymers which are easy to synthesize, especially by methods suitable for mass production, show good structural organization and film-forming properties, exhibit good electronic properties, especially a high charge carrier mobility, a good processibility, especially a high solubility in organic solvents, and high stability in air. Especially for use in OPV cells, there is a need for OSC materials having a low bandgap, which enable improved light harvesting by the photoactive layer and can lead to higher cell efficiencies, compared to the polymers from prior art.
It was an aim of the present invention to provide compounds for use as organic semiconducting materials that are easy to synthesize, especially by methods suitable for mass production, which show especially good processibility, high stability, good solubility in organic solvents, high charge carrier mobility, and a low bandgap. Another aim of the invention was to extend the pool of OSC materials available to the expert. Other aims of the present invention are immediately evident to the expert from the following detailed description.
The inventors of the present invention have found that one or more of the above aims can be achieved by providing conjugated polymers comprising [1,2,5]thiadiazolo[3,4-e]isoindole-5,7-dione (TID) repeating units as electron acceptor units, and one or more electron donor units, wherein these copolymers are random copolymers.
Surprisingly it was found that random donor-acceptor copolymers comprising such TID units provide several advantages. For example, they have an increased solubility profile in common organic solvents (and especially non-chlorinated solvents) leading to better processability, and exhibit a good solid state organisation leading to efficient charge transport. The incorporation of further electron acceptor units in addition to the TID units in the polymer backbone can lead to increased light absorption. WO 2012/149189 A2 discloses copolymers comprising TID units, but does not disclose random copolymers as disclosed and claimed hereinafter.